Injection device preventing the return of the piston when the safety system is deployed

ABSTRACT

The present invention relates to an injection device (1) comprising: —a body (3) designed to receive a product to be injected, furnished at its distal end with an injection needle (7) and receiving a piston (5) capable of being moved between a storage position and an end-of-injection position under the effect of a distal pressure exerted on a piston rod (8) to the distal end of which it is attached, —means of protecting the injection needle (7) capable of adopting an initial position, during which the injection needle (7) is uncovered, and a final position, in which the said injection needle (7) is covered, —biasing means (26) aiming at moving the said covering element (6) from its initial position to its final position, —immobilization means (16, 31) aiming at keeping the said covering element (6) in its initial position, the said injection device (1) being characterized in that: —the said piston rod (8) comprises at least a first portion (9) and at least one second portion (10) coupled to the said piston (8), the said first and second portions (9, 10) being operatively coupled together and selectively movable together in the distal direction, at least one of said first portion (9) and said second portion (10) being movable in the proximal direction separate from said other one of said first portion (9) and said second portion (10).

This application is a continuation of U.S. patent application Ser. No.12/442,174, filed on Apr. 15, 2010, now U.S. Pat. No. 8,852,159, whichis a National Stage Application under 35 U.S.C. § 371 of PCT ApplicationNo. PCT/IB2007/003782, filed Sep. 19, 2007, the contents of theseapplications being incorporated by reference herein.

The present invention relates to a product injection device,particularly for medical use, such as syringes, particularly furnishedwith a safety system aimed at protecting the injection needle after use.

In this application, the distal end of a component or of a device meansthe end furthest away from the hand of the user and the proximal endmeans the end closest to the hand of the user. Similarly, in thisapplication, the terms “in the distal direction” and “distally” mean inthe direction of the injection, and the terms “in the proximaldirection” and “proximally” mean in the direction opposite to thedirection of injection.

Product injection devices, such as syringes, are well known. Theseinjection devices are usually furnished at their distal end with aninjection needle that is designed to be inserted into the skin of apatient, and through which the product to be injected passes to theinjection site. Normally, these syringes are furnished with a piston rodwhose distal end comprises a piston which, during the injection phaseand under the action of a distal pressure exerted by the user on thepiston rod, pushes the product through the injection needle.

One of the constant problems presented by the injection devices is therisk of accidental pricks likely to occur after the injection.

In order to minimize these risks, it is known practice to furnish thesyringes with means of protecting the needle after injection: theseprotection means may for example be in the form of a sleeve slidingrelative to the syringe and required to cover the needle after theinjection and the withdrawal of the needle from the injection site.

Certain of these protection means must be activated manually, the sleevehaving to be moved manually by the end-user to cover the needle.Consequently, these protection means are not very reliable and not verypractical to use. To remedy these disadvantages, injection devices havebeen designed with protection means that are automatically activated,for example by the movement of the piston rod which, when it reaches apredetermined position, releases the sleeve then deployed withoutadditional manual intervention, by elastic means, for example a springforcing its distal movement at the end of injection.

However, it happens that the automatic protection means are activatedwhile the needle is still in the skin of the patient. In such a case,the sleeve begins to deploy and is then stopped by the skin of thepatient against which it is pressed by the spring. The spring cantherefore not deploy further in the distal direction and tends to deployin the proximal direction, which causes the piston rod, and hence thepiston, to rise again in the proximal direction into the body of theinjection device. In other cases as described hereinafter, the pistonrod is caused to rise again by the means for activating the protectionmeans returning elastically to their initial position.

The user may then be confronted with a problem of reabsorption of theinjected product due to the return movement of the piston rod, and henceof the piston, in the proximal direction. This return movement isusually limited in distance: however, it is sufficient to cause aportion of the product previously injected into the body of the patientto return into the body of the syringe, thereby causing an incorrectdosage of the injected product. The recommended dose of product is notinjected in its totality and serious consequences for the patient mayresult therefrom.

Thus, there is the need for an injection device comprising automaticmeans of protecting the needle making it possible to prevent thephenomenon of the return of the piston in the proximal direction afterinjection, in particular when the injection needle remains at least fora moment in the skin of the patient after the end of the injection andwhen the automatic protection means are activated before it iswithdrawn.

Publication WO 03/068298 A1 describes an injection device provided withautomatic protection means activated by the piston rod when the latterarrives at the end of travel towards the end of the dose. The protectionmeans comprise a covering element held in a sheath by elasticallyflexible lateral lugs designed to be deflected by the head of the pistonrod when the latter arrives at the end of travel. The spring providedfor deploying the covering element is placed between the sheath and thecovering element itself. Thus, if, at the end of injection, while theneedle is still in the injection site, the user stops pressing on thepiston rod, the spring will only have the effect of pressing thecovering element towards the skin of the patient without causing thepiston rod to rise again. Nevertheless, this injection device has themajor disadvantage of not allowing the moment when the protection meansare activated to be controlled. It is therefore difficult, evenimpossible, to perform the injection of the end of the dose followed bythe activation of the protection means. Also, in the majority of casesof use, the covering element is released and pressed against the skinwhen the whole dose of product has not yet been injected. Furthermore,the sheath of this injection device comprises elastically flexibleintermediate lugs placed between the lateral lugs and the head of thepiston rod. When the automatic protection means are triggered, if theuser relaxes the pressure of the piston rod, the intermediate lugsreturn to their undeflected position causing the piston to rise again,hence a risk of reabsorption of the previously injected product.

There is therefore also the need for such an injection device making itpossible to trigger the activation of the protection means at the momentdesired by the user and to ensure that the end of the dose of product isinjected without reabsorption.

Specifically, one of the problems encountered with the automaticprotection means is the risk of activating them prematurely orinadvertently, during their use, even during the manufacture and/orassembly of the injection devices. Another associated risk is that of,after activation of the protection means, no longer being able to injectthe end of the dose. Also, to alleviate these problems, the injectiondevices must be manufactured with extremely tight production tolerancesaimed at the end of the dose coinciding with the activation of theactivation means. These production tolerances are difficult toguarantee; the industrial processes for manufacturing the injectiondevices are thereby complicated and slowed and the injection device ismore costly.

Publication WO 2005/030301 A1 describes an injection device providedwith automatic protection means activated by the piston rod when thelatter arrives at the end of travel towards the end of the dose. Theautomatic protection means comprise a covering element designed to bedeployed by a spring. Before activation, this covering element is keptin the withdrawn position by immobilization means. This injection devicealso comprises means of retaining the covering element. These retentionmeans make it possible to prevent the deployment of the covering elementafter activation of the immobilization means. The retention means arereleased by simply relaxing the distal pressure applied to the pistonrod to allow the deployment of the covering element. This injectiondevice nevertheless does not make it possible to remove the risk ofreabsorption when the user relaxes the pressure on the piston rod beforewithdrawing the injection needle from the injection site.

There is therefore the need for an injection device that prevents thereturn of the piston after injection and that is furnished with needleprotection means that can be activated automatically but only when theend-user so decides, making it possible, after activation of theprotection means, to allow the injection of the end of the dose and thatis easy to manufacture.

The object of the invention is therefore to provide an injection device,particularly a syringe, furnished with needle protection means activatedautomatically at the end of injection but preventing the return of thepiston after injection.

Another object of the invention is to provide such an injection devicewhose automatic protection means cannot be activated inadvertently, thusproviding perfect safety against the risks of accidental pricks.

Another object of the invention is to propose such an injection devicewith automatic protection means making it possible to inject the end ofthe dose and capable of being easily manufactured industrially.

The present invention relates to an injection device comprising atleast:

-   -   a substantially tubular body designed to receive a product to be        injected, the said body being furnished at its distal end with        an injection needle, the said body receiving a piston rod and a        piston capable of moving in the said body between a storage        position and an end-of-injection position and of pushing the        said product through the said injection needle,    -   means of protecting the injection needle comprising at least:    -   an element for covering the said injection needle, the said        covering element being movable relative to the said body between        at least an initial position, in which the injection needle is        uncovered, and a final position, in which the said injection        needle is at least partially covered,    -   biasing means arranged to aim at moving the said covering        element between said initial and final positions,    -   immobilization means arranged to aim at holding the said        covering element in at least one of said initial and final        positions,    -   the said injection device being characterized in that:    -   the said piston rod comprises at least a first portion and a        second portion operatively coupled together and selectively        movable together in the distal direction, at least one of said        first portion and said second portion being movable in the        proximal direction separate from said other one of said first        portion and said second portion.

Document U.S. Pat. No. 4,915,692 describes an injection devicecomprising a piston rod comprising two portions, a rod portion and aportion for connection to the piston. However, the connection portion isnot allowed to move in longitudinal translation relative to the rodportion between two predefined positions.

The injection device according to the invention makes it possible toprevent the piston from moving backwards again when the needleprotection means are triggered at the end of injection, particularlywhen this triggering is performed while the needle is still in theinjection site.

Specifically, because a portion of the piston rod is able to moveproximally separately from the other portion, for example at least overa predetermined distance, the proximal deployment of the biasing meanson the piston rod, when the covering element is pressing against theinjection site, is absorbed by the proximal movement of that portion,this absorption allowing the other portion to be unaffected and remainimmobile relative to the body of the injection device. Thus, theinjection device according to the invention makes it possible to preventthe reabsorption of a portion of the medicine already injected, when theneedle covering element, that is to say the needle protection means,moves into place automatically.

The injection device according to the invention therefore makes itpossible to limit the risks due to a faulty, in particular diminished,administration of the dose of prescribed medicine while offering safeuse.

In an embodiment of the invention, said biasing means are arranged toaim at moving said one of said first portion and said second portion inthe proximal direction separate from said other one of said firstportion and said second portion.

In an embodiment of the invention, the injection device comprises atleast one pressing stop and one complementary pressing stop, one beingprovided on the said first portion, the other on the said secondportion, the said pressing and complementary pressing stops beingarranged so as to be operatively coupled together when said piston rodis moved between said storage position and said end-of-injectionposition.

In an embodiment of the invention, said pressing stop and saidcomplementary pressing stop are arranged no as not to be operativelycoupled together when said at least one of said first portion and saidsecond portion is caused to move in the proximal direction.

In an embodiment of the invention, the injection device comprises atleast one retraction stop and one complementary retraction stop, onebeing provided on the said first portion, the other on the said secondportion, the said retraction and complementary retraction stops beingrespectively offset proximally relative to the said pressing stop andcomplementary pressing stop and being arranged so as to be operativelycoupled together when said at least one of said first portion and saidsecond portion is caused to move in the proximal direction.

In an embodiment of the invention, the injection device comprises asheath at least partly receiving the said body, the said biasing means,and the said immobilization means, said sheath being coupled with thesaid covering element.

In an embodiment of the invention, the covering element is able to adoptan intermediate position, distally spaced apart from said initialposition, and in which said injection needle is uncovered

In an embodiment of the invention, said immobilizing means comprisefirst holding means arranged for holding said covering element in saidinitial position, intermediate holding means arranged for holding saidcovering element in said intermediate position, and final holding meansarranged for holding said covering element in said final position.

In an embodiment of the invention, said first holding means is arrangedso as to be released by one of said first portion and said secondportion when said piston rod and piston are moved toward saidend-of-injection position.

In an embodiment of the invention, said intermediate holding means isarranged so as to be released when said one of said first portion andsaid second portion is caused to move in the proximal direction.

In an embodiment of the invention, said first holding means are placedbetween the said sheath and the said covering element, and saidinjection device comprises automatic activation means arranged toautomatically activate the said intermediate holding means during thedistal movement of the said piston rod and piston from the said storageposition to the said end-of-injection position.

In an embodiment of the invention, the injection device also comprisesmeans of automatically releasing the said first holding means.

In an embodiment of the invention, the injection device comprises atleast one intermediate element placed between the said second portionand the said covering element, the said intermediate element comprisingat least a portion of the said automatic means of releasing the saidfirst holding means and/or the said automatic means of activating thesaid intermediate holding means, the said intermediate element beingcapable of movement with respect to said sheath and of interacting withthe said second portion when the said piston rod and piston movesdistally from the said storage position to the said end-of-injectionposition.

In an embodiment of the invention, said intermediate element alsocomprises at least a portion of automatic means of deactivating the saidintermediate holding means, the said intermediate element being capableof movement with respect to said sheath and of interacting with the saidsecond portion when distal pressure exerted on the said second portionof the said piston rod is relaxed.

In an embodiment of the invention, said first holding means comprise atleast one elastically flexible immobilization lug defining animmobilization hook pressing on at least one immobilization surface, atleast one of the said immobilization lug/immobilization surface beingprovided on the said covering element, the other being provided on thesaid sheath, the said immobilization lug being designed to be deflectedby the said second portion or by the said intermediate element in orderto be disengaged from the said immobilization surface.

In an embodiment of the invention, said intermediate holding meanscomprise at least one elastically flexible retention lug defining aretention hook pressing on at least one retention surface, one of thesaid retention lug/retention surface being provided on the said coveringelement or the said sheath, the other being provided respectively on thesaid sheath or on the said covering element, the said retention lugbeing designed to be deflected by the said second portion or by the saidintermediate element in order to be disengaged from the said retentionsurface.

Preferably, said immobilization lug and the said immobilization hook aresubstantially distally offset relative respectively to the saidretention lug, and to the said retention hook so as to allow apreactivation of the said intermediate holding means prior to therelease of the said first holding means when the said piston movesdistally from the said storage position to the said end-of-injectionposition.

Thus, the release of the said first holding means automatically causesthe activation of the said intermediate holding means: the latter thuskeep the covering element in the intermediate position while the usercontinues to exert a distal pressure on the piston rod. After release ofthe first holding means, the deployment of the covering element istherefore subject to the decision of the end-user to relax the pressureon the piston rod.

In an embodiment of the invention, said intermediate element comprisesat least a ring having at least a leg extending in the proximaldirection, at least a guide lug extending in the distal direction anddefining a longitudinal recess, the said ring also being provided withat least a protrusion extending in the distal direction and defining atleast an external ramp.

In an embodiment of the invention, said sheath comprises at least oneprotrusion defining at least one of the said immobilizationsurface/retention surface.

In an embodiment of the invention:

-   -   the said covering element comprises at least the said retention        lug extending in the proximal direction,    -   the said sheath comprises at least one protrusion defining at        least the said retention surface,    -   the said second portion comprises at least one distal skirt        capable of pressing on, and distally pushing, the said leg under        the action of a distal pressure exerted on the said second        portion between the storage position and the end-of-injection        position, causing the distal movement of the said ring, the said        guide lug causing the said retention lug to flex into the said        recess under the action of this movement, the said retention        hook then pressing on the said retention surface.

In an embodiment of the invention:

-   -   the said covering element comprises at least the said        immobilization lug extending in the proximal direction,    -   the said sheath comprises a protrusion defining at least the        said immobilization surface,    -   the said second portion comprises at least one distal skirt        capable of pressing on, and pushing distally, the said leg under        the action of a distal pressure exerted on the said second        portion between the storage position and the end-of-injection        position, causing the distal movement of the said ring, the said        external ramp, under the action of this movement, causing the        said immobilization lug to flex, the said immobilization hook        then pressing on the said immobilization surface.

In an embodiment of the invention, said ring is arranged, when thedistal pressure exerted on the said second portion is relaxed, in orderto move proximally and cause the said retention lug to be released fromthe said recess, the said retention lug then deflecting and allowing thedistal movement of the said covering element towards its final position.

In an embodiment of the invention, said pressing stop, saidcomplementary pressing stop, said retraction stop, and saidcomplementary retraction stop are arranged so that said second portionis spaced apart from said first portion by a distance D of less than 10mm when said second portion is moved in the proximal direction separatefrom said first portion.

Preferably, said distance D is less than or equal to 5 mm and preferablyless than or equal to 3 mm.

In an embodiment of the invention, said first and second portions areacted upon longitudinally in opposite directions by at least onedeformable element, on that in the said storage position, said pressingstop and complementary pressing stop are operatively coupled together.

In an embodiment of the invention, the said biasing means comprise atleast a spring.

In embodiments of the device of the invention, said at least one of saidfirst portion and said second portion being movable in the proximaldirection separate from each other between a pressing position and aretraction position of the piston rod, said first and second portionsare acted upon longitudinally in opposite directions by at least one ormore elastically deformable elements so that they aim at remaining inone of said pressing position or retraction position, irrespective ofthe position of the injection device in space, when the injection deviceis in the storage position.

In one embodiment of the invention, said first portion and said secondportion are maintained in the pressing position by said at least one ormore elastically deformable elements; when said injection device is inthe storage position.

In another embodiment of the invention, said first portion and saidsecond portion are maintained in the retraction position by said atleast one or more elastically deformable elements; when said injectiondevice is in the storage position.

Such embodiments of the invention, in which the first portion and thesecond portion are maintained in one of the pressing or retractionpositions of the piston rod when the injection device is in the storageposition is very reassuring for the user, who can then handle theinjection device without feeling parts moving within the device.

The present invention will now be described in greater detail with theaid of the following description and the appended drawings in which:

FIG. 1 represents a view, in perspective in partial section, of aninjection device according to the invention,

FIG. 2 is a view in perspective of the piston rod of the injectiondevice of FIG. 1,

FIGS. 3A and 36 are cutaway views in perspective of the piston rod ofthe injection device of FIG. 1, when the pressing stop and thecomplementary pressing stop are operatively coupled one to the other,respectively when the retraction stop and the complementary retractionstop are operatively coupled one to the other,

FIG. 4 is a side view of the injection device of FIG. 1, instart-of-injection position,

FIG. 5 is an exploded view in perspective showing the protection meansand the immobilization means of the injection device of FIG. 1,

FIG. 6A is a side view of the injection device of FIG. 1, duringdeactivation of the first holding means,

FIG. 6B is a view in partial section of the piston rod of the device ofFIG. 6A,

FIG. 7 is a side view of the injection device of FIG. 1 showing thefirst holding means deactivated and the intermediate holding meansactivated,

FIG. 8A is a side view of the injection device of FIG. 1 duringdeactivation of the intermediate holding means,

FIG. 8B is a view in partial section of the piston rod of the injectiondevice of FIG. 8A,

FIG. 9 is a side view of the injection device of FIG. 4 with theprotection means protecting the injection needle,

FIGS. 10A to 10C are schematic views of a piston rod of a variant of thedevice of the invention, respectively before injection, during injectionand after the end of injection,

FIGS. 11A to 11C are schematic views of a piston rod of another variantof the device of the invention, respectively before injection, duringinjection and after the end of injection,

FIGS. 12A to 12C are schematic views of a piston rod of a variant of thedevice of the invention, respectively before injection, during injectionand after the end of injection,

FIGS. 13A to 13C are schematic views of a piston rod of a variant of thedevice of the invention, respectively before injection, during injectionand after the end of injection,

FIGS. 14A to 14C are schematic views of a piston rod of a variant of thedevice of the invention, respectively before injection, during injectionand after the end of injection.

FIG. 1 shows an injection device 1 according to the invention in theend-of-injection position. This injection device 1 comprises a sheath 2capable of receiving a tubular body 3 of an injection apparatus, forexample of a syringe as represented or of any other receptacle such as aphial, this injection apparatus comprising a product to be injected. Thebody 3 is furnished at its distal end with an injection needle 7. Thisinjection needle 7 may be bonded to the distal end or fitted for exampleby means of a Luer-type connector. The body 3 houses a piston 5 that isattached to the distal and of a piston rod 8. The piston 5 may beattached to the piston rod 8 by any means, for example screwing, bondingor other means. The piston rod 8 and the piston 5 are capable of movingin the body 3 between a storage position and an end-of-injectionposition. In particular, under the effect of a distal pressure exertedon the piston rod 8, the piston 5 pushes the product to be injectedtowards the distal end of the body 3 and therefore through the injectionneedle 7.

The injection device 1 of the invention of FIG. 1 also comprises meansof protecting the injection needle 7 provided with a covering element,that is a sleeve 6 in the example shown. This sleeve 6 is capable ofmoving relative to the body 3 so as to be able to adopt at least aninitial position, for example a withdrawn position, as shown in FIG. 1,in which the injection needle 7 is uncovered, or else a final position,for example an extended position, as shown in FIG. 9, in which thesleeve 6 entirely covers the injection needle 7, thus preventing therisks of accidental pricking after use. As will be seen hereinafter, thetravel of the sleeve 6 from its withdrawn position to its extendedposition is, in this example, allowed by the user relaxing the distalpressure exerted on the piston rod 8.

In particular, the movement of the sleeve 6 from its withdrawn positionto its extended position is due to the return to a relaxed state ofpreviously compressed biasing means, for example elastic means. Theseelastic means are, in the example shown, in the form of a spring 26.

As appears more clearly in FIGS. 2 to 3B, the piston rod 8 comprises afirst portion 9 in the form of a rod to the distal end of which isattached a piston 5, and a second portion 10 placed at the proximalportion of the piston rod 8 and forming a head thereto. As explainedhereinafter, the said second portion 10 and the said first portion 9 aremovable in longitudinal translation relative to one another between atleast two predefined positions called respectively the pressing positionand the retraction position.

In embodiments shown on FIGS. 10A to 14C and further describedhereinafter, the first portion and the second portion are acted uponlongitudinally in opposite directions by at least one or moreelastically deformable elements so that they aim at remaining either inthe pressing position or in the retraction position, irrespective of theposition of the injection device in space, particularly when the deviceis in the storage position.

The first portion 9 and the second portion 10 are furnished with radialstops limiting the translation of the second portion 10 relative to thefirst portion 9. For this purpose, the first portion 9 comprises, at itsproximal end, two transverse walls 11, 12 in the form of a proximal disc12 and of a distal disc 11. The proximal face of the distal disc 11forms a pressing stop 11 a defining a pressing position of the secondportion 10 and the distal face of the proximal disc 12 forms aretraction stop 12 a defining a retraction position of the secondportion 10.

The second portion 10 of the piston rod 8 comprises two concentriccylindrical skirts, an inner skirl 13, and an outer skirt 14, connectedtogether by a transverse wall 15 forming a pressing surface allowing theuser to exert a distal pressure on the piston rod 8. The end of theinner skirt 13 forms a complementary pressing stop 13 a designed toreceive the pressure of the pressing stop 11 a in the pressing position.In addition, the inner skirt 13 is furnished on its inner wall with acrank defining a complementary retraction stop 13 b designed to receivethe pressure of the retraction stop 12 a in the retraction position. Asappears in FIG. 3A, under the effect of a distal pressure exerted on thepressing surface 15 of the piston rod 8 by a user, the said secondportion 10 is kept in a pressing position by keeping the complementarypressing stop 13 a of the inner skirt 13 of the said second portion 10in contact on the said pressing stop 11 a made on the said first portion9. Because the first and second portions 9, 10 are thus abutting oneanother, the operation of the injection device 1 according to theinvention in no way differs from the injection devices of the prior art,at least as far as the start of the proper injection phase is concerned.The user therefore has no need to modify his mode of operation.

In particular, as will appear further on, the first portion 9 and thesecond portion 10 are operatively coupled together thus, as explainedhereinabove, they are selectively movable together in the distaldirection but at least one of them is movable in the proximal directionseparate or independent from the other. In the example shown, the secondportion 10 is able to move in the proximal direction independently fromthe first portion 9, for example at least on a predetermined distance.As shown on FIG. 3B, the pressing stop 11 a, the complementary pressingstop 13 a, the retraction stop 12 a, and the complementary retractionstop 13 b are arranged so that the second portion 10 is spaced apartfrom the first portion 9 by a distance D of less than 10 mm when thesecond portion 10 is moved in the proximal direction separate from thefirst portion 9. The distance D is preferably less than or equal to 5 mmand more preferably less than or equal to 3 mm.

More particularly, the pressing stop 11 a and the complementary pressingstop 13 a are operatively coupled one to the other. Nevertheless, whenthe second portion 10 is caused to move in the proximal direction, thepressing stop 11 a and the complementary pressing stop 13 a are notoperatively coupled one to the other (cf. FIG. 8B). But in thisretraction position, the retraction stop 12 a and the complementaryretraction stop 13 b are operatively coupled one to the other.

In FIG. 3B, the second portion 10 of the piston rod 8 is in itsretraction position. This retraction position may be reached, as will bedetailed hereinafter, under the action of elastic means (not shown inFIG. 3B) exerting a proximal pressure on the said second portion 10 ofthe piston rod 8, in particular on the distal end 14 a of its outerskirt 14, and keeping the complementary retraction stop 13 b of theinner skirt 13 pressing against the retraction stop 12 a of the disc 12of the first portion 9 of the piston rod 8.

In FIG. 4, the injection device 1 according to the invention is shown ininitial position before injection and the injection needle 7 is stillcovered by a cap 4.

As shown in FIGS. 4 and 5 and as will appear more clearly in FIGS. 6Aand 7, the injection device 1 comprises first holding means forimmobilizing the sleeve 6 in its withdrawn position during at least thebeginning of a phase, called the injection phase, and this is soirrespective of whether the pressure exerted on the piston rod 8 isincreased or relaxed. These first holding means comprise twolongitudinal protrusions 31 provided on the inner surface of the wall ofthe sheath 2 and two elastically flexible immobilization lugs 16extending axially in the proximal direction from the proximal end of thesleeve 6. Preferably, the protrusions 31 are diametrically opposed. Eachprotrusion 31 comprises, at its proximal end, an immobilization surface31 a provided in relief and each immobilization lug 16 is furnished atits proximal end with an immobilization hook 16 a whose distal face 16 bis capable of resting on the immobilization surface 31 a of theprotrusion 31 placed opposite. As will be explained hereinafter, thesefirst holding means for immobilizing the sleeve 6 are capable of beingreleased automatically during the injection, the said sleeve 6 beingthen kept in the intermediate position, in which the injection needle 7is uncovered, by intermediate holding means described hereinafter.

As shown in FIGS. 4 and 5 and as will appear more clearly in FIGS. 6Aand 7, the injection device 1 also comprises intermediate holding meansfor retaining the sleeve 6 in its intermediate position during at leastthe end of the injection phase, after automatic release of the firstholding means. These intermediate holding means comprise the twolongitudinal protrusions 31 previously described. Accordingly, eachlongitudinal protrusion 31 comprises at its proximal end a retentionsurface 31 b provided in relief. The intermediate holding means alsocomprise two elastically flexible retention lugs 17, extending axiallyin the proximal direction from the proximal end of the sleeve 6. Eachretention lug 17 is furnished at its proximal end with a retention hook17 a whose distal face 17 b is capable of pressing on the retentionsurface 31 b of the protrusion 31 placed opposite.

In the example described, each protrusion 31 comprises an immobilizationsurface 31 a and a retention surface 31 b placed in the extension of oneanother. In other embodiments not shown, the injection device maycomprise a protrusion provided with a retention surface and animmobilization surface that are at a distance. Likewise, the injectiondevice may comprise one or more retention protrusions and one or moredistinct immobilization protrusions, each retention protrusioncomprising only one or more retention surfaces, each immobilizationprotrusion comprising only one or more immobilization surfaces.

As will be explained hereinafter, in the example described:

-   -   at the start of injection, the intermediate holding means for        retaining the sleeve 6 are in an inactive position in which the        retention lug 17 is at rest, flexed laterally, the retention        hook 17 a therefore not being in the alignment of the protrusion        31: the distal face 17 b of the hook 17 a is therefore not        engaged with the retention surface 31 b of the protrusion 31 and        does not retain the distal translation of the sleeve 6, this        translation then still being prevented by the first holding        means,    -   during injection, more precisely towards the end of the        injection, the intermediate holding means move to a        preactivation position: more precisely, the retention lug 17 is        straightened under stress so that the retention hook 17 a comes        in the alignment of the protrusion 31 without however pressing        on this protrusion,    -   then, the first holding means are released, the sleeve 6 moves        distally over a short distance until the distal face 17 b of the        retention hook 17 a comes to press on the retention surface 31 b        of the protrusion 31: the intermediate holding means are then in        the active position and prevent the distal translation of the        sleeve 6, the sleeve 6 being than in the intermediate position,    -   at the end of injection, the intermediate holding means are        deactivated by relaxing the pressure applied on the second        portion 10 which, acted upon by the spring 26, moves proximally,        releasing, via an intermediate element described hereinafter,        the retention lug 17 which flexes to its rest state, then        disengaging the retention hook 17 a from the protrusion 31 and        allowing at the end of injection the movement of the sleeve 6        from its intermediate position to its final position.

In another embodiment not shown, the intermediate holding means forretaining the sleeve are, at the outset, in an active position. Theretention lug is then engaged with the protrusion and the injectiondevice comprises active means of releasing this retention lug at the endof injection. In such an embodiment, the sleeve directly moves from itsinitial position to its final position without adopting an intermediateposition.

To improve the grip of the immobilization hook 16 a and retention hook17 a respectively on the immobilization surface 31 a and retentionsurface 31 b of the protrusion 31, the distal faces 16 b and 17 b andthe immobilization face 31 a and retention face 31 b may be providedinclined.

As appears in FIGS. 4 and 5, the injection device 1 also comprises anintermediate element, namely a ring 18 situated in the extreme proximalportion 35 of the sheath 2. The extreme proximal portion 35 of thesheath 2 comprises coupling lugs 32, each coupling lug 32 comprising aradial crank 32 a whose distal face 32 c is designed to retain theproximal face of the ring 18 in the proximal direction, the said radialcrank 32 a comprising an internal ramp 32 b whose function will beexplained hereinafter. The ring 18 is capable of moving relative to thesheath 2, inside the extreme proximal portion 35 of this sheath 2,between the distal faces 32 c of the coupling lugs 32 and of the rims33. The ring 18 comprises means of interaction with the second portion10 of the piston rod 8 of the injection device 1. In the example shown,these interaction means are presented in the form of two diametricallyopposed legs 20 extending in the proximal direction, slightly offset inthe radial direction relative to the body 21 of the ring 18 andconnected at the proximal end of the ring 18 by radial bridges 22.

As will appear more clearly in FIGS. 6A to 9, the ring 18 also comprisesmeans of activating the intermediate holding means in the form, in theexample shown, of the guide lugs 19 extending distally and placedsubstantially symmetrically on the ring 18. Each guide lug 19 defines alongitudinal recess 25 designed to receive a retention lug 17 in activeposition. Each guide lug 19 is provided at its distal end with anactivation ramp 19 a designed to facilitate the flexing and theinsertion of the retention lug 17 into the longitudinal recess 25 whenthe intermediate holding means travel from their inactive to activeposition. The ring 18 also comprises means of releasing the firstholding means, in the form, in the example shown, of a surface 23protruding radially from the body 21 of the ring 18, this surface 23being capable of interacting with the immobilization lugs 16 in order toflex them circumferentially. In the example shown, this surface 23 hasan external ramp 24 opposite each immobilization lug 16.

The proximal end of the spring 26 presses on the distal end 18 a of thering 18 (see FIG. 5) and its distal end presses on an annular rim 28made on the inner surface of the sleeve 6 at its proximal end.

To facilitate assembly, the sheath 2 may be provided in two portionsfixed together during the assembly, for example by snap fitting, bondingor any other equivalent technique.

In practice, the injection device 1 according to the invention is in theinitial position before injection as shown in FIG. 4. In this position:

-   -   the second portion 10 of the piston rod 8 is in the pressing        position (see FIG. 3A),    -   the immobilization lugs 16 are engaged with the immobilization        surfaces 31 a provided in relief,    -   the spring 26 is in an at least partially compressed state. The        system is thus perfectly locked, with no risk of triggering the        activation of the sleeve 6.

To proceed with the injection, the user takes hold of the injectiondevice 1 as shown in FIG. 4, removes the cap 4, applies the injectiondevice 1 to the injection site 104 (see FIG. 6A), inserts the injectionneedle 7 in the injection site 104 and exerts a distal pressure on thepiston rod 8, in particular on the pressing surface 15 of the secondportion 10 of the piston rod 8.

During this injection phase, under the effect of the distal pressureexerted by the user on the pressing surface 15, the second portion 10 ofthe piston rod 8 is kept in its pressing position, as shown in FIG. 6B.In this pressing position, the distal end 13 a of the inner skirt 13 ofthe second portion 10 of the piston rod 8 is abutting, and therefore isoperatively coupled with, the pressing stop 11 a made on the firstportion 9 of the piston rod 8.

Thus, under the effect of the distal pressure exerted by the user on thepressing surface 15 of the second portion 10 of the piston rod 8, thewhole piston rod 8, namely the first portion 9 and the second portion 10together and operatively coupled one to the other, moves in the distaldirection and the first portion 9 pushes the piston 5 towards the distalend of the body 3, thus injecting the product.

As is clear from FIG. 4, during the beginning of this injection phase,the first holding means for immobilizing the sleeve 6 in its initial orwithdrawn position remain locked. Thus, the sleeve 6 is kept in itswithdrawn position by the first holding means irrespective of the valueof the distal force exerted by the user on the piston rod 8. Inparticular, thanks to the first holding means, the sleeve 6 remains inthe withdrawn position, even if the user relaxes the distal pressurethat he exerts on the piston rod 8 via the pressing surface 15.

Towards the end of the injection, while the injection needle 17 is stillinserted into the injection site 104, as shown in FIG. 6A, the secondportion 10 of the piston rod 8 of the injection device 1 comes intocontact with the ring 18. In particular, the distal end 14 a of theouter skirt 14 of the second portion 10 of the piston rod 8 comes intocontact with the interaction means, that is to say the legs 20, in theexample shown, of the ring 18. By continuing to exert a distal pressureand pushing on the second portion 10 of the piston rod 8, the distal end14 a of the outer skirt 14 of the second portion 10 of the piston rod 8pushes the legs 20 of the ring 18 and the ring 18 is thus moved in thedistal direction. Under the effect of this distal movement of the ring18, the activation ramps 19 a of the guide lugs 19 of the sleeve 6straighten the retention lugs 17 and force them into the longitudinalrecesses 25 so that the hooks 17 a are in the trajectory of theprotrusions 31 and the intermediate holding means can immobilize thedistal translation of the sleeve 6. Successively, the external ramps 24of the radial protrusion 23 of the intermediate ring 18 deflect theimmobilization lugs 16 circumferentially so that they are no longerengaged with the protrusions 31.

Thus, the first holding means for immobilizing the sleeve 6 in itswithdrawn position are released and, under the pressure of the spring26, which tries to return to its relaxed state, the sleeve 6 is moved inthe distal direction, over a very short distance, until the distal faces17 a of the retention lugs 17 make contact with the retention surfaces31 b of the protrusions 31 as shown in FIG. 7. The sleeve 6 is then keptin its intermediate position, which is still a withdrawn position of thesleeve 6 in which the injection needle 7 is uncovered, by theintermediate holding means, so long as the user exerts his pressure onthe piston rod 8. In this position, the piston (not visible in FIGS. 6Aand 7) is almost at the end of travel in the body 3.

To terminate the injection, the user prolongs the distal movement of thepiston rod 8 until the piston 5 reaches the bottom of the body 3. Theinjection of the end of the dose is thus assured.

Throughout the injection phase, the user exerts a distal pressure on thesecond portion 10 of the said piston rod 8 that is thus kept in itspressing position, as shown in FIG. 6B.

In normal use, once the end of the dose has been assured, the user keepsthe pressure on the piston rod 8 and withdraws the injection needle 7from the injection site 104. It is nevertheless possible that, throughlack of training, information or attention, the user relaxes thepressure on the piston rod 8 before withdrawing the injection needle 7from the injection site 104. With other injection devices comprisingautomatic protection means activated by the movement of the piston rod,this incorrect use would have the effect of causing a reabsorption ofthe previously injected product, hence an incorrect dose. Specifically,the injection devices of the prior art usually comprise a spring placedbetween the sleeve and the piston rod which, after activation of theprotection means, if the injection needle is still in the injection siteand the sleeve is immobilized by the skin of the patient, causes thepiston rod to return and hence a reabsorption phenomenon.

The invention makes it possible to remove this problem. Specifically,if, while the injection needle 7 is still inserted in the injection site104, and the protection means, namely the covering element or sleeve 6in the example shown, have been activated, the user relaxes the pressurethat he was exerting on the piston rod 8, in particular on the secondportion 10, the ring 18 is moved in the proximal direction under theeffect of the pressure of the spring 26. Accordingly, the surface 23protruding radially from the body 21 of the ring 18 releases theretention lugs 17 from the longitudinal recesses 25 as shown in FIG. 8A.These retention lugs 17 resume their initial, slightly inclined positionrelative to the longitudinal axis of the injection device 1 and thedistal retention faces 17 b of the hooks 17 a are no longer engaged withthe retention surfaces 31 b of the protrusions 31. The proximal movementof the ring 18 at the same time causes, via the legs 20 that push thedistal end 14 a of the outer skirt 14 of the second portion 10 of thepiston rod 8 in the proximal direction, the proximal movement of thissaid second portion 10.

Furthermore, since the injection needle 7 is kept in the injection site104, the sleeve 6 cannot move in the distal direction because it isimmediately stopped by the surface of the skin of the patient.

However, due to the ability of the second portion 10 of the piston rod 8to move in the proximal direction separately from said first portion 9,the first portion 9 of the piston rod 8 remains immobile, at least untilthe second portion 10 reaches its retraction position.

Thus, the ring 18 continues to move in the proximal direction under theaction of the spring 26, and pushes the said second portion 10 of thepiston rod 8. The second portion 10 may thus move to a retractionposition whose end position is delimited by the retraction stop 12 amade on the first portion 9, as shown in FIG. 8B.

During this step, the first portion 9 of the piston rod 8 has not moved.Specifically, because of the particular design of this piston rod 8, theenergy of deployment of the spring 26 which, with other injectiondevices would have caused the reabsorption of the injected product, ishere totally absorbed by the proximal movement of the second portion 10of the piston rod 8 independently from the first portion 9, from itspressing position to its retraction position. Consequently, the firstportion 9 of the piston rod 8 has remained immobile and the piston 5,which is connected thereto, has not moved either. In particular, it hasnot been subjected to a return movement. The risk of reabsorption ofmedicine has thus been prevented.

Preferably, the distance separating the pressing position of the secondportion 10 of the piston rod 8 from its retraction position, that is tosay the distance separating the first portion 9 from the second portion10 when the latter has moved in the proximal direction, is sufficient toabsorb the beginning of deployment of the spring 26. For example, thisdistance, symbolized by the letter D in FIGS. 6B and 8B, may be from 1to 10 mm. Preferably, this distance is less than or equal to 5 mm, stillpreferably less than or equal to 3 mm.

The user may then choose to withdraw the injection needle 7 from thepatient at that moment only.

Under the effect of the pressure of the spring 26, the sleeve 6 is thenmoved in the distal direction and comes to cover the injection needle 7that is shown in dot-and-dash lines in FIG. 9. Then final holding means(not shown), such as legs, provided on the sheath or on the sleeve,capable of engaging recesses provided on the sleeve, respectively on thesheath, immobilize the sleeve in this final position.

With reference to FIGS. 10A to 14C are shown variant embodiments ofpiston rods suitable for the device of the invention.

In particular, with reference to FIGS. 10A to 11C are shown embodimentsof a piston rod in which the first portion and the second portion areacted upon longitudinally in opposite directions by one or moreelastically deformable elements so that they aim at remaining in thepressing position, irrespective of the position of the injection devicein space, when the injection device is in the storage position.

With reference to FIG. 10A is shown schematically a piston rod 8 havinga first portion 9 and a second portion 10. The proximal part of thesecond portion 10 is made of an elastically deformable cover 40. Thiselastically deformable cover may be made out of a material such asplastic, metal, etc. The elastically deformable cover 40 is such that itacts upon said first and second portions (9,10) so that they aremaintained in the pressing position of the piston rod 8, as shown onFIG. 10A, when the injection device (not shown) is in its storageposition, before use. On FIG. 10B is shown the position of the pistonrod 8 during injection. The distal pressure exerted by the user (shownby arrow F on FIG. 10B) allows the injection to be completed but is notimportant enough to deform the cover 40 at that stage. At the end ofinjection, when the user releases the distal pressure he exerted on thepiston rod 8, the second portion 10 is pushed in the proximal direction(represented by arrows P on FIG. 10C) by the ring 18 and the spring 26as explained before for FIGS. 6-8. The force exerted by the spring 26 onthe second portion 10 via the ring 18 is sufficient to deform theelastically deformable cover 40. As shown on FIG. 10C, the deformationof the elastically deformable cover 40 allows the second portion 10 tomove in the proximal direction with respect to the first portion 9 andthe piston rod 8 is now in its retraction position.

FIGS. 11A to 11C show a variant of the embodiment of FIGS. 10A to 10C inwhich the elastically deformable cover is replaced by at least twoelastically deformable strings 50 located between the first portion 9and the second portion 10. The operation of the piston rod 8 of FIGS.11A to 11C is identical to that of FIGS. 10A to 10C. On FIG. 11A, theinjection device (not shown) is in its storage position, before use andthe piston rod 8 is in its pressing position thanks to the elasticallydeformable strings 50 acting upon said first and second portions (9, 10)On FIG. 11B, the piston rod 8 is still in its pressing position duringinjection. On FIG. 11C, the force exerted by the spring 26 has deformedthe strings 50 and the second portion 10 has moved in the proximaldirection with respect to the first portion 9: the piston rod 8 is inits retraction position.

With reference to FIGS. 12A to 14C, are shown embodiments of a pistonrod 8 in which the first portion 9 and the second portion 10 are actedupon longitudinally in opposite directions by one elastically deformableelement (60, 70, 80) so that they aim at remaining in the retractionposition, irrespective of the position of the injection device in space,when the injection device is in the storage position.

With reference to FIG. 12A is shown schematically a piston rod 8 havinga first portion 9 and a second portion 10. An elastically deformabletape 60 is located between the first portion 9 and the second portion10. This elastically deformable tape may be made out of a material suchas plastic, metal, etc. The elastically deformable tape 60 is such thatit acts upon said first and second portions (9,10) so that they aremaintained in the retraction position of the piston rod 8, as shown onFIG. 12A, when the injection device (not shown) is in its storageposition, before use. On FIG. 12B is shown the position of the pistonrod 8 during injection. The distal pressure exerted by the user (shownby arrow F on FIG. 10B) overcomes the resistance to deformation of thetape 60 which deforms as shown on FIG. 12B, allowing the second portion10 to move distally with respect to the first portion 9. The piston rod8 is there in its pressing position and the injection is allowed to becompleted. At the end of injection, when the user releases the distalpressure he exerted on the piston rod 8, the second portion 10 is pushedin the proximal direction (represented by arrows P on FIG. 12C) by thering 18 and the spring 26 as explained before for FIGS. 6-8. The forceexerted by the spring 26 on the second portion 10 via the ring 18 issufficient to bring the elastically deformable tape 60 to its initialstate of FIG. 12A. As shown on FIG. 12C, the return of the elasticallydeformable tape 60 to its non deformed state allows the second portion10 to move in the proximal direction with respect to the first portion 9and the piston rod 8 is now back in its retraction position.

FIGS. 13A to 13C show a variant of the embodiment of FIGS. 12A to 12C inwhich the elastically deformable tape is replaced by an elasticallydeformable cushion 70 located between the first portion 9 and the secondportion 10. The operation of the piston rod 8 of FIGS. 13A to 13C isidentical to that of FIGS. 12A to 12C. On FIG. 13A, the injection device(not shown) is in its storage position, before use and the piston rod 8is in its retraction position thanks to the elastically deformablecushion 70 acting upon said first and second portions (9, 10) On FIG.13B, the piston rod 8 is now in its pressing position, the elasticallydeformable cushion 70 is in its deformed state, the second portion 10has moved in the distal direction with respect to the first portion 9and the injection takes place. On FIG. 13C, the force exerted by thespring 26 has caused the return of the elastically deformable cushion 70to its non deformed state and the second portion 10 has moved in theproximal direction with respect to the first portion 9: the piston rod 8is in its retraction position.

FIGS. 14A to 14C show a variant of the embodiment of FIGS. 12A to 13C inwhich the elastically deformable tape and cushion are replaced by anelastically deformable strip 80 located between the first portion 9 andthe second portion 10. The operation of the piston rod 8 of FIGS. 14A to14C is identical to that of FIGS. 12A to 13C. On FIG. 14A, the injectiondevice (not shown) is in its storage position, before use and the pistonrod 8 is in its retraction position thanks to the elastically deformablestrip 80 acting upon said first and second portions (9, 10) On FIG. 14B,the piston rod 8 is now in its pressing position, the elasticallydeformable strip 80 is in its deformed state, the second portion 10 hasmoved in the distal direction with respect to the first portion 9 andthe injection takes place. On FIG. 14C, the force exerted by the spring26 has caused the return of the elastically deformable strip 80 to itsnon deformed state and the second portion 10 has moved in the proximaldirection with respect to the first portion 9: the piston rod 8 is inits retraction position.

The advantage of embodiments of the piston rod 8 described in FIGS. 10Ato 14C above is that there is no natural possible movement between thefirst and the second portions when the injection device is in itsstorage position, irrespective of the position of the injection devicein space this absence of natural movement between two parts of theinjection device when the user handles the injection device in whateverposition is reassuring for the user.

It is evident from the foregoing that the invention provides determinantenhancements over the similar injection devices of the prior art, bymaking it possible to prevent the proximal return of the piston at theend of injection while the injection needle is still in the injectionsite and after the protection means have been activated. The inventionmakes it possible to benefit from an injection device having automaticprotection means white guaranteeing the possibility of injecting thewhole dose of product without, for all that, requiring a complexmanufacturing method. Specifically, the distance D makes it possible toabsorb the dimensional variations.

It goes without saying that the invention is not limited to theembodiment described hereinabove as an example, but that, on thecontrary, it embraces all the variant embodiments entering the field ofprotection defined by the claims appended hereto.

For example, the invention may be applied to other injection devicessuch as that described in introduction in publication WO 03/068298 A1.In this case, because of the particular design of the piston rod 8according to the invention, the return energy of the intermediate lugsto their rest position after relaxing the distal pressure exerted on thepiston rod 8 is totally absorbed by the movement of the second portion10 of the piston rod 8 from its pressing position to its retractionposition. Consequently, the first portion 9 and the piston 5 remainimmobile and the risk of reabsorption of medicine is thus prevented.

The invention also applies to all the injection devices in which thedeformable elastically flexible lugs are replaced for example by:

-   -   inelastic and/or pivoting lugs, acted upon laterally by elastic        elements,    -   posts travelling in grooves and acted upon laterally by elastic        elements,    -   an additional rotary element, such as for example a collar        placed between the intermediate ring and the covering element,        this collar being provided with grooves capable of receiving        tabs provided on the covering element and forming means of        retention or of immobilization, this collar being free to pivot.

The invention claimed is:
 1. Injection device comprising: a bodydesigned to receive a product to be injected, the body having a distalend with an injection needle, the body receiving a piston rod and apiston capable of moving in the body between a storage position and anend-of-injection position and of pushing the product through theinjection needle, a cover for the injection needle, the cover beingmovable relative to the body between a use position, in which theinjection needle is uncovered, and a final position, in which theinjection needle is at least partially covered, and a spring for movingthe cover between the use and final positions, wherein the piston rodcomprises a first portion, in the form of a rod having the pistonlocated at a distal end thereof, and a second portion, located adjacentto a proximal end of the rod, operatively coupled together andselectively movable together in the distal direction, at least one ofthe first portion and the second portion being movable in the proximaldirection separate from the other one of the first portion and thesecond portion, wherein, with the cover being in the use position, uponsufficient distal advancement of the piston rod, the second portionmoves a predetermined distance in the proximal direction relative to thefirst portion.
 2. Injection device according to claim 1, wherein thefirst portion moves distally continuously with distal advancement of thepiston rod.
 3. Injection device according to claim 1, further comprisinga ring configured to be acted against by the second portion. 4.Injection device according to claim 3, wherein the spring acts againstthe cover and against the ring.
 5. Injection device according to claim3, wherein the ring releases the cover from the use position to allowthe spring to urge the cover towards the final position.